The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Hydraulic motor vehicle transmissions, that is, automatic transmissions for passenger cars and light duty trucks having a plurality of gear assemblies controlled by clutches and brakes, generally include a dedicated hydraulic pump, which provides pressurized transmission (hydraulic) fluid to control valves and actuators. These control valves and actuators engage the clutches and brakes and provide the various gear ratios or speeds.
Such dedicated pumps are generally fixed displacement pumps such as vane or gear pumps that are driven at engine speed from the hub of the torque converter or other startup device located between the engine and the transmission. Such pumps have many design goals. Since the pump is constantly driven at engine speed, it is desirable that it have high efficiency. Additionally, since the pump is most frequently mounted concentric to the engine axis, small size, particularly axial length, is desirable in order not to increase the length of the transmission.
In vehicles having engine stop-start where the engine shuts down during stops in order to increase fuel economy, the pump must be operable to prime or position the clutches and/or brakes by keeping the clutch hydraulic circuits filled with low pressure hydraulic fluid. Various solutions have been proposed to allow the pump to prime the hydraulic circuit during an engine stop-start, such as using auxiliary pumps or accumulators. However, typical designs sacrifice packaging, energy consumption, noise pollution, cost and/or complexity to achieve their goals. Accordingly, there is room in the art for a transmission pump system that has efficient packaging while having reduced complexity and energy costs while still providing adequate engine stop-start performance in terms of energy usage and noise.